1. Field of the Invention
This invention relates to a process and apparatus for measuring an axial eye length in which monochromatic coherent light, of which wavelength varies is projected onto an eyeball to be tested. Reflected light from a retina of the eye is interfered with reference light corresponding to the retina to obtain interference signals while reflected light from a cornea of the eye interferes with reference light corresponding to the cornea to obtain interference signals. These interference signals are mixed to produce beat signals while varying the wavelength, and an axial eye length is obtained based on the beat signals.
Further, this invention relates to a process and apparatus for measuring an axial eye length in which a laser beam emitted from a laser source of which oscillation wavelengths vary is split into measuring laser beam of light and reference laser beam of light. The measuring laser beam of light is projected onto the eye, and light reflected from the cornea of the eye interferes with light reflected from the retina of the eye. The axial length of an eye is obtained based on the interference light.
2. Description of the Prior Art
Heretofore, there has been an apparatus for measuring an axial eye length in which coherent light emitted from a laser diode is projected onto an eye to be tested, reflected lights from the retina and cornea interfere with each other for photoelectric transfer, and an axial eye length is calculated based on photoelectric transfer signals.
However, the conventional apparatus has drawbacks in that too strong coherent light must not be projected onto the eye because it causes inflammations of the retina or damage thereto, intensive interference light cannot be obtained because the reflectances of the retina and cornea are lower, or adequate photoelectric transfer signals in S/N (signal-to-noise) ratio cannot be obtained because the photoelectric transfer signals based on the interference light are too weak. Further, the photoelectric transfer signals are inconstant due to the optically coarse surface of the retina, and a clear distinction between the signals and noises is seldom made due to a weakness of the signals. Hence it is difficult to measure the axial eye length accurately.